This invention is directed to a laser surgery device and method controlled by interferometry.
Laser surgery methods include ophthalmic procedures, dental procedures and irradiation of tissue for hemostasis, photodynamic destruction of forms of tumors, removal of epidermal growths and abnormalities and for the ablation of atherosclerotic plaques. Lasers have been used in surgical procedures to cut tissue and to immediately coagulate the cut. Lasers have been used to control bleeding during surgical removal of burn wound eschar and in surgery on highly vascularized organs such as the liver.
Typically in laser surgery, heat generated by the laser is harnessed to destroy tissue. While thermal effects are commonly used in medical surgical methods, other nonthermal effects are utilized as well. Photons from laser beams can drive chemical reactions, break atomic bonds that hold molecules together or create shock waves to achieve various surgical objectives. Biomedical applications include such tasks as unclogging obstructed arteries, breaking up kidney stones, clearing cataracts and altering genetic material.
Most laser surgical methods utilize the laser heat effect. If the wavelength of light from the laser is matched very closely with the absorption band of the target structure, the laser light will be absorbed by, and therefore damage only that structure. The heat effect of the laser can be extremely selective and precisely controlled. However, in many surgical methods, it is difficult or impossible to choose an irradiating wavelength that will damage target tissue without affecting surrounding tissue. The absorption wavelength of target tissue may not be known or cannot be determined because of turbidity of tissue or other reasons. The absorption band of target tissue may not be distinguishable from the absorption wavelength of surrounding tissue.
U.S. Pat. No. 4,672,963 to Barken, proposes an automated and integrated system for laser surgery. The position of a laser light guide transmitting laser radiation to selected internal structures is controlled by monitoring through the use of an ultrasonic probe. The ultrasonic probe is coupled to a computer system for providing a multiplicity of cross-section images of the internal body structure. By varying the position of the ultrasonic probe along a known longitudinal dimension, a three-dimension image of the structure is reconstructed from two-dimensional images. The images are interpreted by a computer system or by a computer system in conjunction with a physician to control the parameters of a surgical procedure.
However, the use of ultrasonics to control laser surgery is limited. An ultrasonics procedure requires separate insertion of an ultrasonic probe. For example in the surgical procedure for removal of a prostate gland, an ultrasonic probe is entered in the patient transrectally and a laser probe is entered in the patient intraurethrally. Another problem is that ultrasonics cannot be utilized to construct images of very small structures or smaller elements of larger structures and cannot be utilized to detect certain tissue mass that is located within turbid tissue or within tissue having like sonic characteristics to the target tissue.
The present invention relates to a method of laser surgery that permits detection and distinguishing of structures 10 microns in size and smaller. The method permits control of laser surgery without requiring an intrusive probe. The method permits detection of tissue mass that is located within turbid tissue or within tissue having sonic characteristics that are identical to the characteristics of target tissue mass.
The invention provides a method and device for laser surgery wherein a treatment laser beam is controlled by interferometry, preferably by optical coherence tomography. The method comprises detecting a surface or mass of biological tissue by a process of interferometry and controlling the laser treating of the biological tissue according to the detected surface or mass.
The device comprises a laser beam irradiator for applying a laser beam to a target region of biological tissue and an interferometer for projecting a light beam onto the target region. The interferometer includes a detector for receiving a reflected interference beam from the target region, detecting a phase difference of the interference beam and providing an electrical signal according to the phase difference. The device includes a controller responsive to the electrical signal for controlling an output of applied laser beam from the laser beam irradiator.
The method can comprise projecting an interference light beam onto a multilayer target of biological tissue, detecting the interference light beam reflected by the multilayer target to provide an interferogram, evaluating the multilayer target on the basis of the interferogram, and controlling the laser treating of the biological tissue according to the evaluating step.
In another embodiment, the method comprises projecting a phase modulated measurement beam onto a target of biological tissue and projecting a reference beam onto a reference target, combining a reflected reference beam reflected from the reference target with a reflected measurement beam reflected by the target of biological tissue, evaluating a phase difference between the reflected reference beam and the reflected measurement beam and controlling the laser treating of the biological tissue according to the evaluating step.